Useful Reamer Sizes?

[flion]

Yeah, I forgot about the gear tower reamer. That's the only decimal reamer I have; those bolts take a lot of force and you want them as snug as practical; I'm surprised that we don't use close-tolerance bolts there. I can't think of any other areas (other than the spars which are pre-reamed for us) that needs to be that precise. If you're using a reamer, you are probably making holes with sufficient quality to avoid the wallowing problem. For instance, I reamed my brake mount to axle and bolted it with the supplied AN bolt and there is no noticeable slop. But, hey, we can never have enough tools, amiright?

[Rick6a]

Originally Posted by FlyingArcher

.....Please feel free to comment....

Daniel,

If I was a waiter in a restaurant, I'd tell you your menu choice is excellent. Obviously, you understand the fundamentals and your reamer choices reflect that. A reamer is overkill for holes that will be filled with solid rivets, a drill bit serves just fine. As to how many steps to prepare a bolt hole prior to making the final pass with a reamer, there is no hard and fast rule. It depends on how large the hole is, how ambitious you are and what drill bits you happen to have on hand. For a larger diameter hole, I might use 3 or 4 different drill sizes first. Let's say we are drilling out that 5/16" rear spar wing attach bolt hole. Locate and pilot using a #40 or #30. Then I might bring it up to 3/16" then 1/4" then the last drill bit I would use would be either a 19/64" (.2969) or an N drill (.3020) the choice depending if the reamer is piloted or not. The idea is to enlargen the hole in the ballpark of full size yet still leave enough material for the reamer to be effective. That's 4 separate drill passes right there. Of course the final reaming for that critical hole will be with a .310 or .311 using lots of Boelube or similar. I prefer using a slow turning cordless drill for most bolt hole drilling operations. YMMV.

You'll do fine.

[tgmillso]

Maybe I'm overthinking this, however I just wanted to clear up what was necessary to drill the engine mount 3/8" holes to final size (I have already drilled them to 1/4" and am currently using bushings).
3/8" is 0.375, and I have a 0.372 and 0.373 reamer. My concern is what drill should I be using? The closest letter drill size is U (0.368"), then I guess I step up to a 0.370 and finally a 0.372 or 0.373 reamer? Going straight from the U size bit to a 0.372 seems too like it may be too much of a size difference for the reamer.
Cheers,
Tom

[BillL]

Originally Posted by tgmillso

Maybe I'm overthinking this, however I just wanted to clear up what was necessary to drill the engine mount 3/8" holes to final size (I have already drilled them to 1/4" and am currently using bushings).
3/8" is 0.375, and I have a 0.372 and 0.373 reamer. My concern is what drill should I be using? The closest letter drill size is U (0.368"), then I guess I step up to a 0.370 and finally a 0.372 or 0.373 reamer? Going straight from the U size bit to a 0.372 seems too like it may be too much of a size difference for the reamer.
Cheers,
Tom

Nah - it will work just fine unless it is very hard material. I just made some eccentric bushings for my tip up and the 1/4" hole was reamed more than that ( 1/64th). Easily. Make sure it is straight, and if piloted (best for hand reaming) the pilot will be the determining factor. I would not try to hand ream a hole w/o a pilot or a jig for alignment.

It's building, not assembly, so check your process on some non flying material and see how the numbers work in real life. Just a good standard practice anyway. I have learned the hard way not to use untested processes on flight hardware.

[tgmillso]

Thanks Bill. I ordered a U bit and piloted 0.371 reamer, so I should be good to go.
Tom.

[snopercod]

Just a dumb question: If you want a close fit on the larger size holes, why not use Close Tolerance (AN173/174/175) bolts which are ground to +0.0000 / -0.0005?

[MonkeyWrench]

Originally Posted by Rick6a

Here is a fundamental thought:

There is absolutely no reason to purchase an oversize reamer if you don't have an immediate need to use one. Rework or repair is one thing, but we are talking about new construction best practices. To those builders who report bolts eventually wallowing out gear tower holes, I'd have to openly question their drilling technique. That wallowing can often be the result of dimensional slop built into the hole in the first place. We know that too many builders make the final full size pass through bolt holes using a common drill bit. That sorry practice is an unqualified, utterly indefensible no-no. This is sheet metal 101. Always use a reamer to make the final pass through bolt holes, close tolerance or not. There are no ifs ands or buts about it, period. If ever there was a hard and fast rule, this is it.

My personal choice of reamers is influenced by the rigid construction standards central to my former production experience. In that environment, every hole you ever drill is inspected for hole quality. As homebuilders, we don't have to be that strict with ourselves. Still, as a rule I seek as snug a bolt fit as practical. For that reason, when preparing a 3/16" bolt hole, my first choice is a .1870 reamer. If that proves too tight, I up it to .1875. For a 1/4" bolt hole, I try to use a .2490 reamer when I can get away with it but more often than not a .2495 or .2497 reamer to make the final full size pass. For the highly critical wing attach rear spar 5/16" bolts, in addition to using a bushing block which is always good practice, I prepare those holes with a .310 or .311 reamer.

I know those are relatively uncommon reamer dimensions but most builders have ready access to nominal size reamers available everywhere. At the very least, it should become second nature for all airplane builders to use a reamer for making the final full size pass through every bolt hole they ever produce.

Hi All, I know this is an old post, but it is a good one. If i have a whole that gets an AN3 bolt, i believe that is 3/16ths. But, the Van's plans call for a #12 final drill. Should i be reaming that with one size smaller than #12 (3/16th)? Or, should i just follow the plans and go with a #12 drill?

How tight is the bolt supposed to be. I have two other AN3 holes that I can push the threaded part mostly through the hole, but had to tighten the nut to get the rest of the bolt to pull through. Is that ok?

[wirejock]

I typically zhoot for .005" less than the reamer except of course for pre-punched holes.
Seems like Vans calls for a .311" for several holes. I've used it a few times.

[MonkeyWrench]

Opinions Please:

According to the Standard Aircraft Handbook. "A hole that is to be reamed to exact size must be drilled about 0.003- to 0.007-inch undersize. A cut that removes more than 0.007 inch places too much load on the reamer and should not be attempted."
Reference link: https://www.classicaviation.in/uploa...Reithmaier.pdf

In my laymen attempt at figuring this out I was thinking something like this:

Bolt, min" - max", drill at size, and ream at size
AN3, .186 - .189, drill at .181 and ream at .188 (seems most all AN bolts are under .188)
AN4, .246 - .249, drill at .243 and ream at .25 (1/4)
AN5, .309 - .312, drill at .3055 and ream at .3125 (5/16)
AN6, .371 - .374, drill at .368 and ream at .375 (3/8)

.311, drill at .307 and ream at .311

Bolt dimensions.
http://cardinalmfg.com/Uploads/AN_Bolts.pdf

In emailing from Mike from C.A.T., he stated:
3/16 & 0.188 Drill #13
1/4. Drill “D”
5/16 & 0.311 Drill “M”
3/8 Drill “U”

[Tommy123]

Originally Posted by Rick6a

Here is a fundamental thought:

There is absolutely no reason to purchase an oversize reamer if you don't have an immediate need to use one. Rework or repair is one thing, but we are talking about new construction best practices. To those builders who report bolts eventually wallowing out gear tower holes, I'd have to openly question their drilling technique. That wallowing can often be the result of dimensional slop built into the hole in the first place. We know that too many builders make the final full size pass through bolt holes using a common drill bit. That sorry practice is an unqualified, utterly indefensible no-no. This is sheet metal 101. Always use a reamer to make the final pass through bolt holes, close tolerance or not. There are no ifs ands or buts about it, period. If ever there was a hard and fast rule, this is it.

My personal choice of reamers is influenced by the rigid construction standards central to my former production experience. In that environment, every hole you ever drill is inspected for hole quality. As homebuilders, we don't have to be that strict with ourselves. Still, as a rule I seek as snug a bolt fit as practical. For that reason, when preparing a 3/16" bolt hole, my first choice is a .1870 reamer. If that proves too tight, I up it to .1875. For a 1/4" bolt hole, I try to use a .2490 reamer when I can get away with it but more often than not a .2495 or .2497 reamer to make the final full size pass. For the highly critical wing attach rear spar 5/16" bolts, in addition to using a bushing block which is always good practice, I prepare those holes with a .310 or .311 reamer.

I know those are relatively uncommon reamer dimensions but most builders have ready access to nominal size reamers available everywhere. At the very least, it should become second nature for all airplane builders to use a reamer for making the final full size pass through every bolt hole they ever produce.

And a drill bushing. I worked the X47B prototype, all titanium all hi looks. We had to sell every hole to inspection. With a hi look the hole needs to be dead nuts straight and within a couple of thousands. All interference fit. The only drill bits we used were to get a starting point hole then we step reamed. They tend to get mad when you blow a hole on a milled piece of titanium that costs $100,000.